Multilayer structures, packages, and methods of making multilayer structures

ABSTRACT

Multilayer structures, methods of making the same and packages made therefrom are provided. The multilayer structures are useful for packaging bone-in meat or other like products. More specifically, the multilayer structures have sufficient rigidity and strength to contain bone-in meat or other like products. In addition, multilayer structures can easily seal to themselves or to other structures. Moreover, the multilayer structures are biaxially oriented and heat-shrinkable.

This is a Continuation Application of U.S. patent application Ser. No.10/735,134, filed Dec. 12, 2003 now abandoned, which claims priority toU.S. Provisional Patent Application No. 60/453,641, filed Mar. 11, 2003and U.S. Provisional Patent Application No. 60/452,747, filed Mar. 7,2003, each of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

Multilayer structures, methods of making the same and packages madetherefrom useful for packaging products, such as bone-in meat, cheeseand other like products are provided. More specifically, the presentinvention relates to multilayer structures, methods of making the same,and packages made therefrom useful for bone-in meat packaging, cook-inpackaging, shrink film packaging, packaging for case ready meats,hot-fill applications, pet food, retort or lidding, and other likepackaging. The multilayer structures are coextruded and have sufficientdurability, strength, tear resistance and puncture resistance. Inaddition, the present invention relates to multilayer structures,methods of making the same, and packages made therefrom useful forpackaging that is biaxially oriented so as to be heat-shrinkable aroundproducts.

BACKGROUND

It is generally known to utilize thermoplastic multilayer structures,such as films, sheets or the like, to package products. For example,typical products packaged with thermoplastic multilayer structuresinclude perishable products, such as food. Specifically, meats andcheeses are typically packaged in thermoplastic structures. In addition,it is generally known that cook-in structures may be utilized to packagefood products, whereby the products are then heated to cook the foodproducts contained within the packages. Moreover, shrink films are knownfor packaging food products, such as meat and cheese.

One type of meat that may be packaged within thermoplastic multilayerstructures is bone-in meat. Bone-in meat products often contain sharpbones that protrude outwardly from the meat. Typical cuts of bone-inmeat include a half carcass cut, hindquarter cut, round with shank,bone-in shank, full loin, bone-in ribs, forequarter, shoulder and/orother like cuts of meat. When bone-in meat products are packaged and/orshipped, the protruding bones often can puncture or tear the packagingmaterials. This puncturing or tearing of the packaging material by theprotruding bones can occur at the initial stage of packaging or at thelater stage of evacuation of the packaging, which may expose the bone-inmeat products to moisture or other atmospheric conditions, therebyhaving deleterious effects on the bone-in meat product.

Many techniques and products have been developed for preventing bonepuncture or tear. U.S. Pat. No. 6,171,627 to Bert discloses a bagarrangement and packaging method for packaging bone-in meat using twobags to provide a double wall of film surrounding the cut of meat forbone puncture resistance.

U.S. Pat. No. 6,015,235 to Kraimer discloses a puncture resistantbarrier pouch for the packaging of bone-in meat and other products.

U.S. Pat. No. 6,183,791 to Williams discloses an orientedheat-shrinkable, thermoplastic vacuum bag having a protectiveheat-shrinkable patch wherein the heat-shrinkable patch substantiallycovers all areas exposed to bone, thereby protecting the bag frompuncture.

U.S. Pat. No. 5,020,922 to Schirmer discloses a seamless punctureresistant bag which includes a length of lay-flat seamless tubular filmfolded to a double lay-flat configuration. The configuration forms aseamless envelope with one face thickened integrally to triplethickness.

U.S. Pat. No. 5,534,276 to Ennis discloses an oriented heat-shrinkable,thermoplastic vacuum bag having a protective heat-shrinkable reverseprinted patch attached to the bag.

The art teaches many techniques for addressing the problem of bonepuncture or tear in the packaging of bone-in meat products. Many of thesolutions typically include a film structure or bag having patches,double-walled thicknesses or the like. However, a need exists formultilayer structures that may be utilized for packaging bone-in meatproducts and other like products that have sufficient durability,strength, and puncture resistance so as to keep the multilayerstructures from being punctured by bony protrusions from the meat, andyet is heat-sealable so as to form packaging that can seal to themselvesor other structures. In addition, there exists a need in the art foreconomical and commercially viable multilayer structures to formheat-sealable and heat-shrinkable packages for bone-in meat products.

One solution for packaging bone-in meat entails the utilization ofcoextruded multilayer structures having sufficient strength, durability,tear resistance, puncture resistance, and optical properties. However,the formation of coextruded multilayer structures having theseproperties is difficult without laminating the structures to providedouble-walled structures and/or laminating or otherwise adhering patchesto the structures. Laminating structures together to form double-walledstructures or otherwise adhering patches to the structures requiresmultiple complicated processes, thereby requiring additional time andmoney.

For example, known coextruded structures that may be useful for thepresent invention require very thick coextrusions to provide adequatepuncture resistance for bone-in meat. This requires the use of largequantities of fairly expensive polymeric materials to provide theprotection against puncture and tearing. This problem is typicallysolved, as noted above, by laminating structures together to formpatches in the areas of the structures most susceptible to breaking orpuncturing. These patches, while allowing the use of less thermoplasticmaterial, can be unsightly in that the surface of the films areinterrupted by the patches. In addition, the lamination process ofadding the patches to the films can cause decreased opticalcharacteristics, in that patches can become hazy or yellow. Moreover,the areas of the patches also suffer from decreased optical propertiesdue to the thicknesses of the patches and the patches tend to interferewith the shrink characteristics of the structures. Still further, theapplication of the patches requires extra steps in addition to the stepsof making the structures, including precisely positioning the patcheswhere bony protrusions are likely to be.

In addition, many coextruded structures having the durability andstrength to package bone-in meat have sealability problems. As notedabove, the structures must be fairly thick to provide adequate punctureresistance. Typically, heat-sealing bars are utilized to seal thestructures together. If a structure is too thick, the sealing bars willhave difficulty in transferring an adequate amount of heat to theheat-sealing layers to melt the heat-sealing layers of the structures toprovide adequate heat-seals. Inadequate heat-seals cause leaks, therebyexposing products contained within packages made from the structures tomoisture or other atmospheric conditions, which may deleteriously affectthe products.

In addition, thicker structures tend to have a decrease in opticalproperties compared to relatively thinner structures. A structure'sthickness is directly related to haze. Thicker structures, therefore,tend to have an increase in haze, thereby contributing to a decrease inthe clarity of the structures. In addition, thicker structures tend tobe more difficult to orient. Thicker structures tend to have a lowershrink energy, thereby requiring an increase in orientation ratio toprovide similar shrink characteristics as compared to thinnerstructures.

A need, therefore, exists for coextruded multilayer structures havingsuperior strength, durability, tear resistance and puncture resistancethat are significantly thinner than known structures while maintainingsuperior optical properties, such as low haze, low yellowness, and highclarity. In addition, a need exists for coextruded multilayer structuresthat are orientable to provide packages that are heat shrinkable aroundproducts. In addition, coextruded multilayer structures are neededhaving superior sealability as compared to known structures, while stillmaintaining the superior strength, durability, puncture resistance, tearresistance and optical properties. In addition, methods of making themultilayer structures and packages made therefrom are needed.

SUMMARY

Multilayer structures, methods of making the same and packages madetherefrom useful for packaging products, such as bone-in meat, cheeseand other like products are provided. More specifically, the presentinvention relates to multilayer structures, methods of making the same,and packages made therefrom useful for bone-in meat packaging, cook-inpackaging, shrink film packaging, packaging for case ready meats,hot-fill applications, pet food, retort or lidding, and other likepackaging. The multilayer structures are coextruded and have sufficientdurability, strength, tear resistance and puncture resistance. Inaddition, the present invention relates to multilayer structures,methods of making the same, and packages made therefrom useful forpackaging that is biaxially oriented so as to be heat-shrinkable aroundproducts.

Multilayer structures, methods of making the same and packages madetherefrom are provided. More specifically, the multilayer structures canbe utilized for packaging products having bony protrusions or the likethat would easily tear or puncture other structures.

To this end, in an embodiment of the present invention, a multilayerstructure for packaging bone-in meat is provided. The multilayerstructure comprises an outer layer comprising a blend of linear lowdensity polyethylene and low density polyethylene, a first polyamidelayer comprising a blend of between about 70% by weight and about 99% byweight semi-crystalline polyamide and about 1% by weight to about 30% byweight amorphous polyamide, a first tie layer disposed between saidouter layer and said first polyamide layer, a second tie layer disposedadjacent said first polyamide layer, a second polyamide layer disposedadjacent said second tie layer comprising a blend of between about 70%by weight and about 99% by weight semi-crystalline polyamide, andbetween about 1% by weight and about 30% by weight amorphous polyamide,a sealant layer comprising a blend of linear low density polyethyleneand low density polyethylene wherein said volume percent of said heatsealant layer is greater than the volume percent of said outer layer,and a third tie layer disposed between said sealant layer and saidsecond polyamide layer.

Moreover, the first and second polyamide layers each may comprise ablend of between about 85% by weight and about 99% by weightsemi-crystalline polyamide and between about 1% by weight and about 15%by weight amorphous polyamide. Alternatively, said first and secondpolyamide layers each may comprise a blend of between about 60% byweight and about 80% by weight of a first semi-crystalline polyamide,between about 10% by weight and about 30% by weight of a secondsemi-crystalline polyamide, and between about 1% by weight and about 30%by weight amorphous polyamide. The first and said second polyamidelayers may comprise about an equal percent by weight of the multilayerstructure. Moreover, the sealant layer may be between about 25% byvolume and about 30% by volume of the multilayer structure and the outerlayer may be between about 15% by volume and about 20% by volume of themultilayer structure.

In addition, the multilayer structure may be oriented. Further, themultilayer structure may be annealed. Still further, the multilayerstructure may be moisturized by the application of water to saidmultilayer structure. The multilayer structure may further beplasticized. In addition, the multilayer structure may be irradiated topromote crosslinking between the layers of said multilayer structureand/or within a layer of said multilayer structure.

Further, all layers of the multilayer structure of the presentembodiment may be coextruded to form said multilayer structure.Preferably, the multilayer structure may be between about 1 mil andabout 8 mils thick. Most preferably, the multilayer structure may bebetween about 1.5 mils and about 5 mils thick.

In an alternate embodiment of the present invention, a package forbone-in meat is provided. The package comprises a first wall comprisinga multilayer structure comprising an outer layer comprising a blend oflinear low density polyethylene and low density polyethylene; a firstpolyamide layer comprising a blend of about 70% by weight to about 99%by weight semi-crystalline polyamide and about 1% by weight to about 30%by weight amorphous polyamide; a first tie layer disposed between saidouter layer and said first polyamide layer; a second tie layer disposedadjacent to said first polyamide layer; a second polyamide layerdisposed adjacent said second tie layer comprising a blend of about 70%by weight to about 99% by weight semi-crystalline polyamide and about 1%by weight to about 30% by weight amorphous polyamide; a sealant layercomprising a blend of linear low density polyethylene and low densitypolyethylene wherein the volume percent of said heat sealant layer isgreater than the volume percent of said outer layer; and a third tielayer disposed between said sealant layer and said second polyamidelayer.

In addition, the package further comprises a bone-in meat product withinthe package and the multilayer structure may be heat-shrunk around saidbone-in meat product.

The first and second polyamide layers each may comprise a blend ofbetween about 85% by weight and about 99% by weight semi-crystallinepolyamide and between about 1% by weight and about 15% by weightamorphous polyamide. Alternatively, the first and second polyamidelayers each may comprise a blend of between about 60% by weight andabout 80% by weight of a first semi-crystalline polyamide, between about10% by weight and about 30% by of a second semi-crystalline polyamide,and between about 1% by weight and about 30% by weight amorphouspolyamide. The first and second polyamide layers may comprise about anequal percent by weight of the multilayer structure.

Moreover, the sealant layer may be between about 25% by volume and about30% by volume of the multilayer structure and the outer layer may bebetween about 15% by volume and about 20% by volume of the multilayerstructure.

In addition, the multilayer structure of the package of the presentinvention may be oriented and heat-shrinkable. Further, the multilayerstructure may be annealed at a temperature. Still further, themultilayer structure may be moisturized by the application of water tosaid multilayer structure. Moreover, the multilayer structure may beirradiated to promote crosslinking between the layers of said multilayerstructure and/or within a layer of said multilayer structure. Inaddition, the multilayer structure may be plasticized and all the layersof the multilayer structure may be coextruded to form the multilayerstructure.

Preferably, the multilayer structure of the package of the presentinvention may be between about 1 mil and about 8 mils thick. Mostpreferably, the multilayer structure of the package of the presentembodiment may be between about 1.5 mils and about 5 mils thick. Thepackage may further be in the form of a tube having a space therein forbone-in meat. Alternatively, the first wall may be heat-sealed to asecond wall wherein the first wall and the second wall form a space forbone-in meat.

In another alternate embodiment of the present invention, a method ofmaking a multilayer for packaging bone-in meat is provided. The methodcomprises the steps of coextruding a multilayer structure comprising anouter layer comprising a blend of linear low density polyethylene andlow density polyethylene wherein said outer layer comprises betweenabout 15% by volume and about 20% by volume of the multilayer structure;a first polyamide layer comprising a blend of between about 80% byweight and about 99% by weight semi-crystalline polyamide and about 1%by weight to about 20% by weight amorphous polyamide; a first tie layerdisposed between said outer layer and said first polyamide layer; asecond tie layer disposed adjacent said first polyamide layer; a secondpolyamide layer disposed adjacent said second tie layer comprising ablend of between about 80% by weight and about 99% by weightsemi-crystalline polyamide, and between about 1% by weight and about 20%by weight amorphous polyamide; a sealant layer comprising a blend oflinear low density polyethylene and low density polyethylene whereinsaid sealant layer comprises between about 25% by volume and about 30%by volume of the multilayer structure; and a third tie layer disposedbetween said sealant layer and said second polyamide layer; andbiaxially orienting said multilayer structure.

The method of the present embodiment further comprises the step ofannealing said multilayer structure at a temperature of between about60° C. and about 90° C. Still further, the method of the presentembodiment comprises the step of irradiating said multilayer structureto promote crosslinking between the layers of said multilayer structureand/or within a layer of said multilayer structure. The method furthercomprises the step of moisturizing said multilayer structure by applyingwater to said multilayer structure.

Moreover, the sealant layer may be between about 25% by volume and about30% by volume of the multilayer structure and the outer layer may bebetween about 15% by volume and about 20% by volume of the multilayerstructure.

Preferably, the multilayer structure of the method of the presentembodiment may be between about 1 mil and about 8 mils thick. Mostpreferably, the multilayer structure of the method of the presentembodiment may be between about 1.5 mils and about 5 mils thick.

Multilayer structures and packages made from multilayer structures areprovided that can be easily and cost-effectively manufactured. Morespecifically, the multilayer structures can be made via coextrusion ofthe layers together. The multilayer structures are, therefore, easy toproduce and can be made quickly and efficiently.

In addition, multilayer structures and packages made from the multilayerstructures are provided that can be oriented, thereby providingincreased strength, especially when utilized as packaging for bone-inmeat products and the like.

Moreover, multilayer structures and packages made from the multilayerstructures are provided having superior strength, durability, tearresistance and puncture resistance while being significantly thinnerthan known coextruded structures having comparable strength, durability,tear resistance and puncture resistance. Thinner coextruded multilayerstructures have the additional advantages of having superior opticalproperties, such as low haze and yellowness. In addition, thinnercoextruded multilayer structures have the additional advantage of beingeasily heat-sealable and heat-shrinkable. Still further, thinnerstructures contribute to the utilization of less materials, whichcontributes to cost efficiencies and to a reduction of waste products,both during production of the structures, and after the structures areutilized for packages.

In addition, multilayer structures and package made from multilayerstructures are provided having increased stiffness.

Still further, multilayer structures and packages are provided made frommultilayer structures having improved durability, strength, tearresistance and puncture resistance that may be made by a coextrusionprocess, without needing extra series of steps for laminating otherstructures thereto. Therefore, multilayer structures and packages areprovided that do not have double walls or patches.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the detailed description of thepresently preferred embodiments and from the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a cross-sectional view of a seven-layer structure inan embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Multilayer structures, methods of making the same and packages madetherefrom are provided wherein the multilayer structures are useful forpackaging meat products having bony protrusions and other like productshaving sharp protrusions. The bony protrusions make it difficult toutilize structures without some form of reinforcing material, such as adouble-walled film structure or patches or the like. However, it hasbeen found that a multilayer coextruded structure made withoutdouble-walling or without the use of patches may be formed that hassufficient rigidity, strength, tear resistance and puncture resistanceto hold bone-in meat products.

The methods of the present invention are useful for making multilayerstructures for packaging meat products having bony protrusions and otherlike products having sharp protrusions. The bony protrusions make itdifficult to utilize structures without some form of reinforcingmaterial, such as a double-walled film structure or patches or the like.However, it has been found that a multilayer coextruded structure madewithout double-walling or without the use of patches may be formed thathas sufficient rigidity, strength, tear resistance and punctureresistance to hold bone-in meat products.

The multilayer structures of the present invention typically have atleast one layer of nylon and a heat-sealant layer that preferably allowsthe structures to be heat-sealed to themselves or to other structures toform packages having a space therein for bone-in meat.

For purposes of describing the layers of the thermoplastic multilayerstructures described herein, the term “inner layer” refers to the layerof a package made from the coextruded multilayer structure that directlycontacts the inner space of the package and/or directly contacts theproduct contained therein, especially when heat-shrunk around theproduct, as described in more detail below. The term “outer layer”refers to a layer of the coextruded multilayer structure disposed on theexternal surface thereof. Specifically, if a package is made from anon-laminated coextruded structure, the outer layer is disposed on theexternal surface of the package.

Typically, the outer layer of the multilayer structures providesrigidity and strength to the film, and further provides protection frompunctures, tears and the like, and is often referred to as an “abuselayer”. Materials that may be useful in the outer layer are thosetypically used for abuse layers in multilayer structures, such as lowdensity polyethylene (“LDPE”), or heterogeneous or homogeneous ethylenealpha-olefin copolymers, such as linear low density polyethylene(“LLDPE”) and medium density polyethylene (“MDPE”) made by typicalpolymeric processes, such as Ziegler-Natta catalysis andmetallocene-based catalysis. Moreover, other ethylene copolymers may beutilized as well, such as ethylene vinyl acetate copolymer (“EVA”) andethylene methyl acrylate copolymer (“EMA”). Other materials may includepolypropylene (“PP”), polyamides, ionomers, polyesters or blends of anyof these materials. In addition, an amount of slip and/or antiblock maybe added to aid the outer layer in forming and to provide desirablecharacteristics.

Preferably, the outer layer comprises a blend of octene-based LLDPE andLDPE. A preferable range of LLDPE and LDPE utilized in the outer layermay be between about 50% by weight and about 90% by weight LLDPE andabout 10% by weight and about 50% by weight LDPE. Most preferably, theblend of LLDPE and LDPE may be about 70% by weight LLDPE and about 30%by weight LDPE. In addition, the blend of the outer layer may comprise asmall amount of antiblock and/or slip agent. Alternatively, the outerlayer may comprise a polyamide or blend of polyamide materials.

In addition, the coextruded multilayer structures of the presentinvention typically have at least one internal layer. An “internallayer” is a layer disposed within a multilayer structure, and is bondedon both sides to other layers. A preferred material that is useful as aninternal layer is a polyamide. Generally, polyamide materials that areuseful for the at least one internal layer include, but are not limitedto, nylon 6, nylon 6,69, nylon 6,66, nylon 12, nylon 6,12, nylon6,IPD,I, amorphous polyamide, or blends of any of these materials.Preferably, the at least one internal layer is a blend of polyamidematerials, such as, for example, a blend of semi-crystalline polyamideand amorphous polyamide, although amorphous polyamide is not necessaryin the at least one internal layer.

For example, the internal layer may comprise nylon 6 or nylon 6,66 andamorphous polyamide, or a blend of nylon 6, nylon 6,69 and amorphouspolyamide. It is preferable to utilize a blend of a large amount ofsemi-crystalline polyamide, such as about 70% by weight to about 99% byweight semi-crystalline polyamide, such as nylon 6 or nylon 6,66 or ablend of nylon 6 and nylon 6,69, with a small amount of amorphouspolyamide, such as between about 1% by weight and about 30% by weightamorphous polyamide. More preferably, the internal layer may compriseabout 85% by weight to about 99% by weight semi-crystalline polyamide,such as nylon 6 or nylon 6,66 or a blend of nylon 6 and nylon 6,69, withabout 1% by weight to about 15% by weight amorphous polyamide. Mostpreferably, the internal layer may comprise about 90% by weight to about99% by weight semi-crystalline polyamide and about 1% by weight andabout 10% by weight amorphous polyamide.

In addition, the polyamide layers of the present invention may comprisea blend of a first semi-crystalline polyamide, a second semi-crystallinepolyamide, and an amorphous polyamide. Specifically, the polyamidelayers may comprise between about 60% by weight and about 80% by weightof the first semi-crystalline polyamide, between about 10% by weight andabout 30% by weight of the second semi-crystalline polyamide, andbetween about 1% by weight and about 30% by weight of the amorphouspolyamide.

The blends described herein allow the internal layer of polyamide toretain softness and ease of processability while still imparting highpuncture resistance, strength and stiffness to the film structure. Inaddition, polyamide blends comprising a small amount of amorphouspolyamide have improved orientation and, therefore, shrinkcharacteristics. Specifically, a small amount of amorphous polyamide inthe polyamide blend with semi-crystalline polyamide improves bothout-of-line orientation and in-line orientation.

Alternatively, the coextruded multilayer structures of the presentinvention may have a plurality of polyamide layers. For example,structures may have an outer layer comprising polyamide and an internallayer comprising polyamide. Alternatively, the structures may have twoor more internal layers of polyamide. The two or more layers ofpolyamide may preferably be separated by an internal core layer, such asa tie layer to bind the two layers of polyamide together. In oneembodiment of the present invention, the two or more layers of polyamidemay be the same polyamide. In another embodiment, the two layers may bedifferent. Preferably, the two or more layers of polyamide areidentical, such as an identical blend of semi-crystalline polyamide andamorphous polyamide.

The internal core layer may be a tie layer. The tie layer may beutilized to bind other layers together, such as the outer layer,heat-sealant layer, and/or polyamide layer or layers. Typically, the tielayer may comprise a modified polyolefin, such as maleic anhydridemodified polyolefin. Polyolefins useful as the internal core layer ofthe present invention include, but are not limited to, anhydridemodified linear low density polyethylene or any other maleic anhydridemodified polyolefin polymers or copolymers, such as anhydride modifiedethylene-vinyl acetate copolymer and/or anhydride modified ethylenemethyl acrylate copolymer. Alternatively, the internal core layer maycomprise a material that is not a tie resin. Specifically, the internalcore layer may comprise a material that is not modified with maleicanhydride, such as ethylene vinyl acetate copolymer and/or ethylenemethyl acrylate copolymer. Other polymeric materials that may be usefulas tie layers include, but are not limited to, an acid terpolymercomprising ethylene, acrylic acid and methyl acrylate, polyamide, andpolystyrene block copolymers. In addition, the internal core layer maycomprise blends of tie resins with other polymeric material, such aspolyolefins or the like.

Preferably, the internal core layer comprises a maleic anhydridemodified ethylene methyl acrylate copolymer, such as, for example,BYNEL® from DuPont. Most preferably, the internal core layer comprisesmaleic anhydride modified linear low density polyethylene, such asADMER® from Mitsui.

The multilayer structures of the present invention may further have aheat-sealant layer that may form heat-seals when heat and/or pressure isapplied to the package. For example, the structures of the presentinvention may be folded over onto themselves and sealed around edges tocreate a package with the bone-in meat products contained therein.Alternatively, the structures may be formed as a tube, whereby ends ofthe tube may be heat-sealed together to create a package for theproduct. Moreover, a first structure of the present invention may bedisposed adjacent a second structure of the present invention and sealedaround edges of the structures to form a package for the bone-in meat orother like products.

The heat-sealant layer materials include, but are not limited to,various polyolefins, such as low density polyethylene, linear lowdensity polyethylene and medium density polyethylene. The polyethylenesmay be made via a single site catalyst, such as a metallocene catalyst,or a Ziegler-Natta catalyst, or any other polyolefin catalyst system. Inaddition, other materials include, but are not limited to,polypropylene, ionomer, propylene-ethylene copolymer or blends of any ofthese materials. Further, acid modified polyolefins and tie resins orconcentrates, such as, for example, anhydride modified polyethylene, maybe utilized in the heat sealant layer, which may be useful for meatadhesion when the multilayer structure is heat shrunk about a bone-inmeat product.

Preferably, the heat-sealant layer of the structure of the presentinvention may comprise a blend of octene-based linear low densitypolyethylene and low density polyethylene. More specifically, theheat-sealant layer may comprise between about 50% by weight and about90% by weight LLDPE and between about 10% by weight and about 50% byweight LDPE. Most specifically, the heat-sealant layer comprises about70% by weight LLDPE and about 30% by weight LDPE. Optionally, theheat-sealant layer comprises a small amount of slip and/or antiblock toaid in the processability of the structures of the present invention.

The above-identified materials may be combined into a structure havingat least three layers that has sufficient puncture resistance, strengthand optical properties to form packages that are useful for packagingbone-in meat or other like products.

The coextruded multilayer structures of the present invention arepreferably coextruded and biaxially oriented via a double bubbleprocess, whereby each layer of each of the multilayer structures iscoextruded as a bubble and then cooled. Typical cooling processesinclude air cooling, water cooling or cooling via non-contact vacuumsizing. The coextruded multilayer structures may then be reheated andoriented in both the longitudinal and transverse directions.Alternatively, the coextruded multilayer structures of the presentinvention may be oriented via other orienting processes, such astenter-frame orientation.

The oriented multilayer structures are then heated to an annealingtemperature and cooled while the multilayer structures maintain theiroriented dimensions in a third bubble, thereby annealing the multilayerstructures to relax residual stress and provide stability and strengthto the multilayer structures while maintaining the heat shrinkabilityand superior optical characteristics of oriented multilayer structures.Use of a third bubble for purposes of annealing the oriented structuresis often referred to as a triple-bubble process. The structures of thepresent invention may be partially or completely annealed. Annealing themultilayer structure allows for precise control over the degree ofshrink and/or over the stability of the multilayer structure, and istypically done at a temperature between room temperature and theanticipated temperature at which the multilayer structure is desired toshrink.

In addition, the multilayer structures of the present invention may befurther processed to get desirable characteristics. For example,multilayer structures of the present invention may be cross-linked viaknown cross-linking processes, such as by electron-beam cross-linkingeither before or after orientation of the multilayer structure.Cross-linking may occur between layers (“inter-layer crosslinking”) ofthe structures or molecularly within at least one layer of a structure(molecular cross-linking”). Any radiation dosage may be utilized topromote inter-layer cross-linking or molecular cross-linking as may beapparent to one having ordinary skill in the art. In addition, thestructures may be moisturized, by exposing the surfaces of thestructures to water so that certain layers of the structures, such asthe polyamide layers, absorb the water thus plasticizing the polyamidelayers, thereby making the polyamide layers softer and stronger.Moisturizing the structures typically occurs by exposing the surface ofthe structures to water, such as a mist, prior to rolling the structuresfor storage. During storage of the structures, the water is absorbed bythe layers of the structures, such as the polyamide layers, therebyplasticizing the structure. Of course, other methods for plasticizingthe structures are contemplated by the present invention, and theinvention should not be limited as described herein.

Preferably, the structures of the present invention have a thickness ofbetween about 1 and about 8 mils. Most preferably, the structures of thepresent invention have a thickness of between about 1.5 mils and about 5mils A balance must be reached between having a cost-effective package,thereby minimizing the thickness of the structures, and having a packagethat provides adequate puncture and tear resistance for bone-in meat orother like products. It is believed that a combination of materials usedin the structures contributes to the advantageous properties of thestructures of the present invention, such as puncture resistance,strength, durability, and optical properties, without requiringrelatively thick structures.

The structures of the present invention are utilized to make heatshrinkable bags, such as by coextruding heat shrinkable tubes, cuttingsaid tubes to the desired sizes, placing product within said tubes,sealing the open ends of the tubes, and heat-shrinking the tubes aroundthe products. Alternatively, packages may be made by folding structuresso that the heat-sealant layers of the structures are in face-to-facecontact. In addition, packages may be made by heat-sealing first wallsof first multilayer structures to second walls of second multilayerstructures to form a space for a product to be contained therein. Ofcourse, any other method of making said packages are contemplated by thepresent invention. Machinery contemplated as being used to make the bagsor packages of the present invention include intermittent motionbag-making machines, rotary bag-making machines, or multibaggers, whichare described in U.S. Pat. No. 6,267,661 to Melville, the disclosure ofwhich is expressly incorporated herein in its entirety.

In a typical bag-making process, tubes are produced using adouble-bubble or a triple-bubble process, as described above. Thesurfaces of the tubes may be lightly dusted with starch. An open end ofthe tube is then heat-sealed with one end of the tube left open foradding the product to the package. Other types of packages and uses arecontemplated by the present invention, such as vertical form, fill andseal packages and lidstock for rigid or semi-rigid trays. In addition,the structures of the present invention may be useful as cook-in bags orthe like.

The tubes then have product placed therein, such as bone-in meat. Thetubes are then evacuated of air and the open end of each is heat-sealed.The tubes that have been evacuated of air and heat-sealed are thenshrunk around the product by sending the tubes through an oven, a hotwater tunnel or other similar heat-shrink apparatus.

As noted above, the structures of the present invention may have atleast three layers, but preferably contain four, five, six or morelayers. Most preferably, the structures comprise seven layers. Inaddition, structures having greater than seven layers are contemplatedby the present invention. Each structure preferably has a heat-sealantlayer, a polyamide layer, and an internal tie layer. Moreover, it ispreferable to have at least two layers of polyamide contained withineach of the structures disposed on opposite sides of the internal tielayer thereby bonding the internal tie layer to the other layers withineach of the multilayer structures.

The following non-limiting example illustrates a five-layer structure ofthe present invention:

Example 1

Percent by volume Materials and percent Structure Layer of structure byweight of layer 1 (Outer layer) 45.0  80% Nylon 6  20% amorphouspolyamide 2 (Tie layer) 5.0 100% anhydride modified LLDPE 3 (Polyamidelayer) 35.0  90% Nylon 6  10% amorphous polyamide 4 (Tie layer) 5.0 100%anhydride modified LLDPE 5 (Sealant layer) 10.0  50% LLDPE  50% LDPE

Example 1 illustrates a five-layer structures of the present invention.Specifically, the five-layer structure comprises an outer layer ofpolyamide, a tie layer of anhydride modified LLDPE, an internal layer ofpolyamide, such that the outer layer of polyamide and the internal layerof polyamide are disposed adjacent to the tie layer of anhydridemodified LLDPE. A second tie layer is disposed adjacent to the internallayer of polyamide, which binds the internal layer of polyamide to thesealant layer of a blend of LLDPE and LDPE.

In a preferred embodiment of the present invention, seven-layercoextruded structures are provided, as illustrated in FIG. 1. Thestructures preferably comprise a first outer layer 10, a first tie layer12, a first polyamide layer 14, a second tie layer 16, a secondpolyamide layer 18, a third tie layer 20 and a sealant layer 22. Each ofthe layers is described in more detail below.

The outer layer 10 of the seven-layer structure illustrated in FIG. 2provides rigidity and strength to the film structure, and furtherprovides protection from scratches, tears and the like. Preferably, theouter layer 10 is between about 5% by volume and about 25% by volume ofthe entire structure. Most preferably, the outer layer 10 comprisesabout 17.5% by volume of the entire structure.

The seven layer structure further comprises a plurality of tie layers.Specifically, the seven layer structure may comprise a first tie layer12, a second tie layer 16, and a third tie layer 18. Although each ofthese tie layers is designated as “first”, “second” or “third”, itshould be noted that these designations are for convenience, and thatany of the tie layers may be referred to as the “first”, “second” or“third” tie layers, depending on the order described. For example, the“first” tie layer may be the tie layer 16, which is disposed between thefirst polyamide layer 14 and the second polyamide layer 18 if the tielayer 16 is the first to be described relative to the other tie layers.In that situation, the “second” tie layer may be tie layer 12 and the“third” tie layer may be tie layer 20. In the instant description of thelayers with respect to FIG. 1, however, the “first” tie layer is the tielayer 12, the “second” tie layer is the tie layer 16, and the “third”tie layer is the tie layer 20, as illustrated in FIG. 1.

The first tie layer 12 and third tie layer 20 of the seven layerstructures of the present invention, which are disposed adjacent theouter layer 10 and the sealant layer 22, respectively, may be utilizedto bind the outer layer 10 or the sealant layer 22 to other internallayers, such as the first polyamide layer 14 and second polyamide layer18. In addition, the second tie layer 16 may split the first polyamidelayer 14 and second polyamide layer 18. The first tie layer 12, secondtie layer 16, and/or third tie layer 20 may comprise modifiedpolyolefins, such as maleic anhydride modified polyolefins. Polyolefinsuseful as the first tie layer 12, second tie layer 16, and/or third tielayer 20 of the present invention include, but are not limited to,anhydride modified linear low density polyethylene or any other maleicanhydride modified polyolefin polymer or copolymer, such as anhydridemodified ethylene-vinyl acetate copolymer and/or anhydride modifiedethylene methyl acrylate copolymer. Alternatively, the first tie layer12, second tie layer 16, and/or third tie layer 20 may comprise amaterial that is not a tie resin. Specifically, the first tie layer 12,second tie layer 16, and/or third tie layer 20 may comprise materialsthat are not modified with maleic anhydride, such as ethylene vinylacetate copolymer and ethylene methyl acrylate copolymer. Otherpolymeric materials that may be useful as tie layers include, but arenot limited to, an acid terpolymer comprising ethylene, acrylic acid andmethyl acrylate, polyamide, and polystyrene block copolymers. Inaddition, the first tie layer 12, second tie layer 16 and/or third tielayer 20 may comprise blends of tie resins with other polymericmaterial, such as polyolefins or the like.

Preferably, the first tie layer 12, the second tie layer 16, and thirdtie layer 20 comprise a maleic anhydride modified linear low densitypolyethylene. Most preferably, the first tie layer 12, second tie layer16 and third tie layer 20 comprise maleic anhydride modified ethylenemethyl acrylate copolymer, such as BYNEL® from DuPont or maleicanhydride modified linear low density polyethylene, such as ADMER™ fromMitsui. It should be noted that the first tie layer 12, second tie layer16, and third tie layer 20 may not be the same material, but may bedifferent materials that are useful for tying together the outer layer10 to an internal layer of, for example, polyamide, the first polyamidelayer 14 to the second polyamide layer 18, and/or the sealant layer 22to an internal film layer of polyamide. Although the first tie layer 12,the second tie layer 16, and third tie layer 20 may be any thicknessuseful for the present invention, it is preferable that the first tielayer 12, second tie layer 16, and third tie layer 20 each comprisebetween about 2% by volume and about 15% by volume of the multilayerstructures. Most preferably, each of the first tie layer 12, second tielayer 16 and third tie layer 20 comprise about 5% by volume of theentire multilayer structures.

The first polyamide layer 14 and/or second polyamide layer 18 may beutilized to provide rigidity and strength to structures made from thepresent invention. The polyamide layers further provide ease oforientation, better shrink force and lower oxygen transmission ratesthrough the multilayer structure. It should be noted that the firstpolyamide layer 14 and second polyamide layer 18 may not be the samematerial, and may be different depending on the desired characteristicsof the structures. In addition, each of the first polyamide layer 14and/or second polyamide layer 18 of the seven layer structures may bebetween about 10% by volume and about 60% by volume of the structuresMore specifically, each of the polyamide layers of the seven layerstructures may be between about 10% by volume and about 40% by volume ofthe structures. Most preferably, each of the polyamide layers of theseven layer structures may be between about 15% and about 25% by volumeof the structures.

The sealant layer 22 of the seven layer structure illustrated in FIG. 1may comprise between about 20% by volume and about 30% by volume of theentire structure. Most preferably, the sealant layer 22 of the presentinvention may comprise about 27.5% by volume of the entire structure,especially when the outer layer 10 comprises about 17.5% by volume ofthe entire structure. It is further preferable that the outer layer 10and the sealant layer 22 comprise different amounts of polymericmaterial, thereby creating an unbalanced structure. If the outer layer10 is thinner than the sealant layer 22, then the entire structurethickness will be thinner, thereby allowing a heat-sealing mechanismsuch as a heat-sealing bar, to heat the sealant layer 22 to melt thesealant layer 22 to form a heat-seal more effectively. In addition,having more polymeric material in the sealant layer 22 allows thesealant layer 22 to melt and flow, thereby forming a strong seal whenheat-sealed to another structure or to itself.

The seven-layer structures of the present invention, as described aboveand illustrated in FIG. 1, are preferably coextruded and orientedthereby producing structures that are heat shrinkable. The totalorientation factor of the seven-layer structures are preferably betweenabout 6 and about 20. More preferably, the total orientation factor isbetween about 8 and about 13. The structures of the present inventionmay further be partially or completely annealed, preferably at atemperature of between room temperature and the temperature at which thestructure is heat shrunk. Annealing the structures stabilizes thestructures by removing residual stresses within the oriented structuresresulting from non-uniform cooling rates during the orientation process.Typically, the structures are maintained in a third bubble and heatedabove their annealing temperatures, thereby providing more stablemultilayer structures.

The following examples illustrate specific embodiments of seven layerstructures:

Example 2

Percent by volume Materials and percent Structure Layer of structure byweight of structure layer 1 (Outer) 22.5  49% LLDPE  49% LDPE  2% blendof slip and antiblock 2 (First Tie) 5.0 100% anhydride modified LLDPE 3(First Polyamide) 20.0  70% nylon 6  25% nylon 6.69  5% amorphouspolyamide 4 (Second Tie) 5.0 100% anhydride modified LLDPE 5 (SecondPolyamide) 20.0  70% nylon 6  25% nylon 6.69  5% amorphous polyamide 6(Third Tie) 5.0 100% anhydride modified LLDPE 7 (Sealant) 22.5  49%LLDPE  49% LDPE  2% blend of slip and antiblock

The seven layer structure of Example 2 was made by coextruding the sevenlayers together and biaxially orienting the resulting structure. Theseven layer structure had a total orientation factor of about 11.7.Further, the structure was annealed to stabilize the structure. Thecoextrusion, orientation, and annealing of the seven layer structure ofExample 2 were completed in a triple bubble process. The final structurethickness was about 3.3 mils.

Example 3

Percent by volume Materials and percent Structure Layer of structure byweight of structure layer 1 (Outer) 17.5  49% LLDPE  49% LDPE  2% blendof slip and antiblock 2 (First Tie) 5.0 100% anhydride modified LLDPE 3(First Polyamide) 20.0  70% nylon 6  25% nylon 6.69  5% amorphouspolyamide 4 (Second Tie) 5.0 100% anhydride modified LLDPE 5 (SecondPolyamide) 20.0  70% nylon 6  25% nylon 6.69  5% amorphous polyamide 6(Third Tie) 5.0 100% anhydride modified LLDPE 7 (Sealant) 27.5  49%LLDPE  49% LDPE  2% blend of slip and antiblock

The seven layer structure of Example 3 was made by coextruding the sevenlayers together and biaxially orienting the structure. The structure hada total orientation factor of about 11.4. In addition, the seven layerstructure of Example 3 was annealed to stabilize the final structure.The coextrusion, orientation, and annealing of the seven layer structureof Example 3 were completed in a triple bubble process. The finalstructure thickness was about 3.7 mils.

This structure of Example 3 is similar to the structure described inExample 2, except that the structure of Example 3 contains differingamounts of materials in the outer layer and the sealant layer.Specifically, the outer layer comprises about 17.5% by volume of thestructure, and the inner sealant layer comprises about 27.5% by volumeof the structure.

Example 4

Percent by volume Materials and percent Structure Layer of structure byweight of structure layer 1 (Outer) 15.0  49% LLDPE  49% LDPE  2% blendof slip and antiblock 2 (First Tie) 5.0 100% anhydride modified LLDPE 3(First Polyamide) 25.0  70% nylon 6  25% nylon 6.69  5% amorphouspolyamide 4 (Second Tie) 5.0 100% anhydride modified LLDPE 5 (SecondPolyamide) 25.0  70% nylon 6  25% nylon 6.69  5% amorphous polyamide 6(Third Tie) 5.0 100% anhydride modified LLDPE 7 (Sealant) 20.0  49%LLDPE  49% LDPE  2% blend of slip and antiblock

The seven layer structure of Example 4 was made by coextruding the sevenlayers together and biaxially orienting the structure. The structure hada total orientation factor of about 9.1. In addition, the seven layerstructure of Example 4 was annealed to stabilize the final structure.The coextrusion, orientation, and annealing of the seven layer structureof Example 4 were completed in a triple bubble process. The finalstructure thickness was about 3.9 mils.

The seven layer structure of Example 4 is similar to the seven layerstructure of Example 3, including differing amounts of materials in theouter layer and the sealant layer. However, the structure of Example 4includes more polyamide material than the structure of Example 3. Morespecifically, polyamide layer in the structure of Example 4 comprisesabout 25% by volume of the structure. The entire structure comprisesabout 50% by volume of polyamide.

Example 5

Percent by volume Materials and percent Structure Layer of structure byweight of structure layer 1 (Outer) 20.0  49% LLDPE  49% LDPE  2% blendof slip and antiblock 2 (First Tie) 5.0 100% anhydride modified LLDPE 3(First Polyamide) 15.0  70% nylon 6  25% nylon 6.69  5% amorphouspolymide 4 (Second Tie) 5.0 100% anhydride modified LLDPE 5 (SecondPolyamide) 15.0  70% nylon 6  25% nylon 6.69  5% amorphous polymide 6(Third Tie) 5.0 100% anhydride modified LLDPE 7 (Sealant) 35.0  49%LLDPE  49% LDPE  2% blend of slip and antiblock

The seven layer structure of Example 5 was made by coextruding the sevenlayers together and biaxially orienting the structure. The structure hada total orientation factor of about 11.9. In addition, the seven layerstructure of Example 5 was annealed to stabilize the final structure.The coextrusion, orientation, and annealing of the seven layer structureof Example 5 were completed in a triple bubble process. The finalstructure thickness was about 4.0 mils.

The seven layer structure of Example 5 is similar to the seven layerstructure of Example 3, including differing amounts of materials in theouter layer and the sealant layer. However, the structure of Example 5includes less nylon material than the film of Example 3. Morespecifically, each polyamide layer in the structure of Example 3comprises about 15% by volume of the structure. The entire structurecomprises about 30% by volume polyamide total.

Example 6

Percent by volume Materials and percent Structure Layer of structure byweight of structure layer 1 (Outer) 17.5  49% LLDPE  49% LDPE  2% blendof slip and antiblock 2 (First Tie) 5.0 100% anhydride modified LLDPE 3(First Polyamide) 20.0  92% nylon 6  8% amorphous polyamide 4 (SecondTie) 5.0 100% anhydride modified LLDPE 5 (Second Polyamide) 20.0  92%nylon 6  8% amorphous polyamide 6 (Third Tie) 5.0 100% anhydridemodified LLDPE 7 (Sealant) 27.5  49% LLDPE  49% LDPE  2% blend of slipand antiblock

The seven layer structure of Example 6 was made by coextruding the sevenlayers together and biaxially orienting the structure. In addition, theseven layer structure of Example 6 was annealed. The coextrusion,orientation, and annealing of the seven layer structure of Example 6were completed in a triple bubble process. The final structure thicknesswas about 4.0 mils. Each of the polyamide layers of the seven layerstructure of Example 6 comprises a blend of about 92% by weight nylon 6and about 8% by weight amorphous polyamide.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages. It is, therefore, intendedthat such changes and modifications be covered by the appended claims.

We claim:
 1. A package comprising a multilayer structure and bone-inmeat, the multilayer structure comprising: an outer layer comprisingpolyethylene wherein the volume percent of the outer layer is between 5%and 25% of the multilayer structure; a first polyamide layer, whereinsaid first polyamide layer comprises a blend of between 91% by weightand 99% by weight semi-crystalline polyamide and 1% by weight to 9% byweight amorphous polyamide, wherein the volume percent of the firstpolyamide layer is between 15% and 25% of the multilayer structure; afirst tie layer disposed between and in contact with each of said outerlayer and said first polyamide layer, wherein the volume percent of thefirst tie layer is between 2% and 15% of the multilayer structure; asecond tie layer comprising polyamide disposed in contact with saidfirst polyamide layer; a second polyamide layer disposed in contact withsaid second tie layer, wherein said second polyamide layer comprises ablend of between 91% by weight and 99% by weight semi-crystallinepolyamide, and between 1% by weight and 9% by weight amorphouspolyamide, wherein the volume percent of the second polyamide layer isbetween 15% and 25% of the multilayer structure; a sealant layer,wherein the sealant layer comprises polyethylene, wherein the volumepercent of the sealant layer is greater than the volume percent of theouter layer; and a third tie layer disposed between and in contact witheach of said sealant layer and said second polyamide layer, wherein thevolume percent of the third tie layer is between 2% and 15% of themultilayer structure, wherein the multilayer structure is biaxiallyoriented, wherein the multilayer structure has a low oxygen transmissionrate due to the first and second polyamide layers, and the packagecomprises a bone-in meat contained therein, where a bone of the bone-inmeat protrudes from the meat and contacts the multilayer structure,wherein the multilayer structure does not comprise a double wall orpatch, is heat-shrinkable, annealed and has rigidity, strength, oxygenbarrier and puncture resistance to hold the bone-in meat.
 2. Themultilayer structure of claim 1 wherein said first and said secondpolyamide layers comprise an equal percent by volume of the multilayerstructure.
 3. The multilayer structure of claim 1 wherein said sealantlayer is between 25% by volume and 30% by volume of the multilayerstructure and the outer layer is between 15% by volume and 20% by volumeof the multilayer structure.
 4. A bone-in meat package comprising: afirst wall comprising a multilayer structure comprising: an outer layercomprising polyethylene wherein the volume percent of the outer layer isbetween 5% and 25% of the multilayer structure; a first polyamide layer,wherein said first polyamide layer comprises a blend of 91% by weight to99% by weight semi-crystalline polyamide and 1% by weight to 9% byweight amorphous polyamide, wherein the volume percent of the firstpolyamide layer is between 15% and 25% of the multilayer structure; afirst tie layer disposed between and in contact with each of said outerlayer and said first polyamide layer, wherein the volume percent of thefirst tie layer is between 2% and 15% of the multilayer structure; asecond tie layer comprising polyamide disposed in contact with saidfirst polyamide layer; a second polyamide layer disposed in contact withsaid second tie layer, wherein said second polyamide layer comprises ablend of 91% by weight to 99% by weight semi-crystalline polyamide and1% by weight to 9% by weight amorphous polyamide, wherein the volumepercent of the second polyamide layer is between 15% and 25% of themultilayer structure; a sealant layer, wherein said sealant layercomprises polyethylene, wherein the volume percent of the sealant layeris greater than the volume percent of the outer layer; a third tie layerdisposed between and in contact with each of said sealant layer and saidsecond polyamide layer, wherein the volume percent of the third tielayer is between 2% and 15% of the multilayer structure; wherein themultilayer structure is biaxially oriented, wherein the multilayerstructure has a low oxygen transmission rate due to the first and secondpolyamide layers, wherein the multilayer structure is heat-shrunk arounda bone-in meat and a bone of the bone-in meat protrudes from the meatand contacts the multilayer structure, and wherein the multilayerstructure is annealed and has rigidity, strength, oxygen barrier andpuncture resistance to hold the bone-in meat and does not comprise adouble wall or patch.
 5. The package of claim 4 wherein said first andsecond polyamide layers comprise an equal percent by weight of themultilayer structure.
 6. The package of claim 4 wherein said sealantlayer is between 25% by volume and 30% by volume of the multilayerstructure and the outer layer is between 15% by volume and 20% by volumeof the multilayer structure.
 7. A method of making a package comprisinga multilayer structure and bone-in meat, the method comprising the stepsof: coextruding a multilayer structure comprising an outer layercomprising polyethylene, wherein the volume percent of the outer layeris between 5% and 25% of the multilayer structure; a first polyamidelayer, comprising a blend of between 91% by weight and 99% by weightsemi-crystalline polyamide and 1% by weight to 9% by weight amorphouspolyamide, wherein the volume percent of the first polyamide layer isbetween 15% and 25% of the multilayer structure; a first tie layerdisposed between and in contact with each of said outer layer and saidfirst polyamide layer, wherein the volume percent of the first tie layeris between 2% and 15% of the multilayer structure; a second tie layercomprising polyamide disposed in contact with said first polyamidelayer; a second polyamide layer disposed in contact with said second tielayer comprising a blend of between 91% by weight and 99% by weightsemi-crystalline polyamide, and between 1% by weight and 9% by weightamorphous polyamide, wherein the volume percent of the second polyamidelayer is between 15% and 25% of the multilayer structure; a sealantlayer comprising polyethylene wherein the volume percent of the sealantlayer is greater than the volume percent of the outer layer; and a thirdtie layer disposed between and in contact with each of said sealantlayer and said second polyamide layer, wherein the volume percent of thethird tie layer is between 2% and 15% of the multilayer structure;biaxially orienting said multilayer structure using a tubular processwhereby each layer of the multilayer structure is coextruded together asa bubble, cooled, then reheated and oriented in both the longitudinaland transverse directions; and annealing said multilayer structure,wherein the multilayer structure has a low oxygen transmission rate dueto the first and second polyamide layers, and placing bone-in meatwithin the package and heat shrinking the package around the bone-inmeat, wherein a bone of the bone-in meat protrudes from the meat andcontacts the multilayer structure, and wherein the multilayer structurehas rigidity, strength, oxygen barrier and puncture resistance to holdthe bone-in meat and does not comprise a double wall or patch.
 8. Themethod of claim 7 wherein the sealant layer is between 25% by volume and30% by volume of the multilayer structure and the outer layer is between15% by volume and 20% by volume of the multilayer structure.
 9. Themethod of claim 7 further comprising a step of irradiating saidmultilayer structure to promote crosslinking between the layers of saidmultilayer structure, prior to the placing step.
 10. The method of claim7 further comprising a step of irradiating said multilayer structure topromote crosslinking within a layer of said multilayer structure, priorto the placing step.
 11. The method of claim 7 further comprising a stepof moisturizing said multilayer structure by applying water to saidmultilayer structure, prior to the placing step.
 12. The method of claim7 wherein the tubular process comprises a double bubble process.
 13. Themethod of claim 12, wherein the multilayer structure is oriented in thesecond bubble of the double bubble process.